Niranjan Karak

A green and facile approach for the synthesis of water soluble fluorescent carbon dots from banana juice

Green luminescent water soluble oxygenous carbon dots with an average size of 3 nm were synthesized by simply heating banana (Musa acuminata) juice at 150 °C for 4 h without using any surface passivating and oxidizing agent or inorganic salt. The literature was used to propose a possible mechanism for the formation of carbon dots by this approach. The resulting carbon dots exhibited concentration, excitation wavelength and pH dependent luminescent behavior in the visible range. The quantum yield was 8.95 on excitation at a wavelength of 360 nm, using quinine sulfate as the reference. The presence of large amounts of oxygenous functionality was confirmed by FTIR and EDX studies. XRD and TEM illustrated the poor crystalline nature and narrow distribution of these spherical carbon dots. Thus bio-based fluorescent carbon dots with a high yield were reported for the first time through a simple and effective route without using any special apparatus or reagents.

Polymer-assisted iron oxide magnetic nanoparticle immobilized keratinase

Nanotechnology holds the prospect for avant-garde changes to improve the performance of materials in various sectors. The domain of enzyme biotechnology is no exception. Immobilization of industrially important enzymes onto nanomaterials, with improved performance, would pave the way to myriad application-based commercialization. Keratinase produced by Bacillus subtilis was immobilized onto poly(ethylene glycol)-supported Fe3O4 superparamagnetic nanoparticles. The optimization process showed that the highest enzyme activity was noted when immobilized onto cyanamide-activated PEG-assisted MNP prepared under conditions of 25 degrees C and pH 7.2 of the reaction mixture before addition of H2O2 (3% w/w), 2% (w/v) PEG(6000) and 0.062:1 molar ratio of PEG to FeCl2 x 4H2O. Further statistical optimization using response surface methodology yielded an R2 value that could explain more than 94% of the sample variations. Along with the magnetization studies, the immobilization of the enzyme onto the PEG-assisted MNP was characterized by UV, XRD, FTIR and TEM. The immobilization process had resulted in an almost fourfold increase in the enzyme activity over the free enzyme. Furthermore, the immobilized enzyme exhibited a significant thermostability, storage stability and recyclability. The leather-industry-oriented application of the immobilized enzyme was tested for the dehairing of goat-skin.

Novel high performance tough hyperbranched epoxy by an A2 + B3 polycondensation reaction

High performance tough epoxy thermoset with excellent adhesive strength is one of the most in demand materials for advanced engineering applications. In the present investigation three hyperbranched epoxy resins with varying compositions were synthesized by a single step controlled polycondensation reaction using an A2 + B3 approach for the first time. The physical properties like epoxy equivalent, hydroxyl value, viscosity, etc. of the synthesized epoxy resins were determined by different analytical techniques. The hyperbranched structure of the resins was characterized by spectroscopic techniques. The degrees of branching were found to be 0.60, 0.79 and 0.51 for the resins with 10, 20 and 30 wt% of the B3 moiety respectively, as obtained from the 13C NMR study. The poly(amidoamine) cured hyperbranched epoxy thermosets exhibited high thermostability (up to 293, 298 and 296 °C), tensile strength (38, 47 and 26 MPa), elongation at break (43, 21 and 52%), strain energy or toughness (1277, 758 and 1056 MPa), exceptionally high adhesive strength (1987, 2662, 1638 MPa), impact resistance (>100 cm) and scratch hardness (8.5, 9.0, 8.0 kg). The results showed the prominent role of the amount of the B3 moiety in the performance of the thermosets. The study, therefore, revealed that the unison of the aliphatic–aromatic moiety in the hyperbranched structure can offer a high performance tough epoxy thermoset without any processing difficulty.

Vegetable Oil-Based Hyperbranched Thermosetting Polyurethane/Clay Nanocomposites

The highly branched polyurethanes and vegetable oil-based polymer nanocomposites have been showing fruitful advantages across a spectrum of potential field of applications.Mesua ferrea L. seed oil-based hyperbranched polyurethane (HBPU)/clay nanocomposites were prepared at different dose levels by in situ polymerization technique. The performances of epoxy-cured thermosetting nanocomposites are reported for the first time. The partially exfoliated structure of clay layers was confirmed by XRD and TEM. FTIR spectra indicate the presence of H bonding between nanoclay and the polymer matrix. The present investigation outlines the significant improvement of tensile strength, scratch hardness, thermostability, water vapor permeability, and adhesive strength without much influencing impact resistance, bending, and elongation at break of the nanocomposites compared to pristine HBPU thermoset. An increment of two times the tensile strength, 6 °C of melting point, and 111 °C of thermo-stability were achieved by the formation of nanocomposites. An excellent shape recovery of about 96–99% was observed for the nanocomposites. Thus, the formation of partially exfoliated clay/vegetable oil-based hyperbranched polyurethane nanocomposites significantly improved the performance.

Bio-based tough hyperbranched polyurethane–graphene oxide nanocomposites as advanced shape memory materials

A fast and simple approach for the large scale fabrication of highly flexible castor oil-modified hyperbranched polyurethane (HPU)–graphene oxide (GO) nanocomposites with high toughness is reported. Three different wt% (0.5, 1 and 2) of GO are incorporated into a HPU matrix to prepare uniformly dispersed GO-based nanocomposites. The performance studies show a tremendous enhancement of the toughness (2540 to 6807 MJ m−3) as well as the increment of tensile strength (7 to 16 MPa), elongation at break (695 to 810%) and scratch hardness (5 to 6.5 kg) on the formation of the nanocomposites with 2 wt% GO. The Halpin–Tsai model suggests the 3D random distribution of GO in the HPU matrix. Thermal properties such as thermostability, melting point, enthalpy, degree of crystallinity and glass transition temperature (Tg) etc. of the nanocomposites are correlated with their shape recovery (∼99.5%) and shape fixity (∼90%) behaviour. Thus, HPU–GO nanocomposites have the potential to be used as advanced thermo-responsive shape memory materials.

Biocompatible epoxy modified bio-based polyurethane nanocomposites: Mechanical property, cytotoxicity and biodegradation

Epoxy modified Mesua ferrea L. seed oil (MFLSO) based polyurethane nanocomposites with different weight % of clay loadings (1%, 2.5% and 5%) have been evaluated as biocompatible materials. The nanocomposites were prepared by ex situ solution technique under high mechanical shearing and ultrasonication at room temperature. The partially exfoliated nanocomposites were characterized by Fourier transform infra-red (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The mechanical properties such as tensile strength and scratch hardness were improved 2 and 5 times, respectively by nanocomposites formation. Even the impact resistance improved a little. The thermostability of the nanocomposites was enhanced by about 40 degrees C. Biodegradation study confirmed 5-10 fold increase in biodegradation rate for the nanocomposites compared to the pristine polymers. All the nanocomposites showed non-cytotoxicity as evident from RBC hemolysis inhibition observed in anti-hemolytic assay carried over the sterilized films. The study reveals that the epoxy modified MFLSO based polyurethane nanocomposites deserve the potential to be applicable as biomaterials.

Multi-stimuli responsive smart elastomeric hyperbranched polyurethane/reduced graphene oxide nanocomposites

In this report, a tough elastomeric hyperbranched polyurethane/reduced graphene oxide (HPU/RGO) nanocomposite was fabricated by an in situ polymerization technique. Reduction of graphene oxide was carried out by a green sonochemical approach using the combined effect of sonication and Fe3+ ions in presence of Colocasia esculenta leaves aqueous extract. The reduction occurred only in 3 min, while 8 min was required without sonication. Prepared RGO and nanocomposites were characterized by different spectroscopic and analytical tools. The nanocomposite demonstrated excellent thermal stability and mechanical properties, such as tensile strength (27.8 MPa), tensile modulus (36.3 MPa) and toughness (116 MJ m−3). The nanocomposite also exhibited outstanding multi-stimuli responsive shape memory behaviour under direct sunlight, microwave (360 W) and heat energy (60 °C). The performance of the nanocomposite was dependent on the loading of RGO (0.5–2.5 wt%). Thus, these nanocomposites have tremendous potential to be used as advanced non-contact triggered smart materials for different applications, including biomedical.

Transparent luminescent hyperbranched epoxy/carbon oxide dot nanocomposites with outstanding toughness and ductility.

A luminescent transparent hyperbranched epoxy nanocomposite with previously unachieved outstanding toughness and elasticity has been created by incorporation of a very small amount of carbon oxide nanodots. The nanocomposites of the hyperbranched epoxy with carbon oxide dots at different dose levels (0.1, 0.5, and 1.0 wt %) have been prepared by an ex situ solution technique followed by curing with poly(amido-amine) at 100 °C. Different characterizations and evaluations of mechanical and optical properties of the nanocomposites have been performed. The toughness (area under the stress-strain curve) of the pristine system has been improved dramatically by 750% with only 0.5 wt % carbon oxide dots. The tensile strength has been enhanced from 38 to 46 MPa, whereas the elongation at break improved noticeably from 15 to 45%. Excellent adhesive strength combined with transparency and photoluminescent behavior renders these materials highly interesting as functional films in optical devices like light-emitting diodes and UV light detection systems as well as in anticounterfeiting applications.

One step preparation of a biocompatible, antimicrobial reduced graphene oxide–silver nanohybrid as a topical antimicrobial agent

A reduced graphene oxide–silver nanohybrid (Ag–RGO) was prepared by simultaneous reduction of graphene oxide and silver ions, using the aqueous extract of the Colocasia esculenta leaf. The nanohybrid demonstrated better antimicrobial activity than the individual nanomaterials. Excellent cytocompatibility was observed for peripheral blood mononuclear cells (PBMCs) and mammalian red blood cells (RBCs). An acute dermal toxicity study on wistar rats confirmed no induction of direct or indirect toxicity to the host. Thus, this nanohybrid holds potential for applications as a non-toxic topical antimicrobial agent in dressings, bandages, ointments etc.

Silver-embedded modified hyperbranched epoxy/clay nanocomposites as antibacterial materials.

Silver-embedded modified hyperbranched epoxy/clay nanocomposites were prepared at different wt.% of octadecyl amine-modified montmorillonite at a constant silver concentration (1 wt.%). UV-visible, XRD and TEM studies confirmed the formation of silver nanoparticles. Compared to the system without silver and clay, the gloss from 70° to 94°, scratch hardness from 4 to 5.8 kg, impact strength from 60 to 90 cm, tensile strength from 8.5 to 15.5 MPa, adhesive strength from 5 to 7.1 × 10(9)N/m, flexibility from >6 to <4mm, and thermostability from 230 to 260 °C increased for the modified system. Resistance to aqueous 10% HCl, 0.5% NaOH, 10% NaCl also increased. The nanocomposites showed antibacterial activity in well diffusion assays against Staphylococcus aureus (ATCC11632), Bacillus subtilis (ATCC11774), Escherichia coli (MTCC40), Pseudomonas aeruginosa (MTCC7814) and Klebsiella pneumoniae (ATCC10031). The results showed that these nanocomposites have potential to be used as antimicrobial materials.